Exotic breathing fast....mouth breathing when he knows I'm near, but he doesn't know I'm here it's normal, already seen 2 vets both say all good, thinking of getting a 3rd opinion.

Grumpy is about 2 yo (appox cat cafe threw him out once they were out of business no papers etc ), adopted him a couple months ago when I first got him he was breathing fast(60+ a min), took him to a vet, other than IBD all good, this was always on my mind so for a peace of mind I took him to another vet a month ago, 2nd vet didn't find anything wrong with him.

We're having a heat wave and for the past 2 days I've caught him mouth breathing, took him to the 1st vet again(closest) he says it's because of the heat.... I've paid close attention to him these past few days & he seems to be breathing normal (<40 per min) when he doesn't know I there? When I say his name or make some noise & he sees me immediately 60+ a min, am I imagining things?

Thinking of getting a 3rd opinion, but every time I take him out he mouth breathes & drools like crazy, I don't wanna put unnecessary stress on him.

Thanks!